Internal combustion engine

ABSTRACT

An internal combustion engine which devises the opened direction and position of the gas outlet end of a sub-suction path provided separately from a main suction path so as to inject a gas in the circumferential direction of a combustion chamber during the suction stroke, in which the outlet end of the sub-suction path opens within such a range that, in a plane normal to the axis of the cylinder, the line extending in an opened direction of the sub-suction path is at an angle of ±20 to 110 degrees with respect to the line joining the center of the suction port and the axis of the cylinder; the distance between the outlet end of the sub-suction path and the face of a suction valve at its closed position is not more than the internal diameter of the main suction path; or the outlet end of the sub-suction path is positioned within a sphere with its center being a spark point of an ignition plug and with the same diameter as the internal diameter of the cylinder and within a range of ±1 mm from the plane which contains both the center line of the stem of the intake valve and such one of the points of tangency between the valve facing circle of the valve seat of the suction valve and the lines drawn from the spark joint of the ignition plug as is nearer to the wall of the cylinder.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an internal combustion engine which isintended to reduce the noxious content of the exhaust gas, especially,nitrogen oxides (NO_(X)) and to improve the mileage.

2. Description of the Prior Art

Recently, in an internal combustion engine for automobiles, not only thepurification of the exhaust gas but also the improvement in the rate offuel consumption are required. For these requirements, an EGR (exhaustgas recirculation) and a lean combustion are frequently performed. Inorder to prevent the combustion fluctuations and the misfire whilesatisfying both the requirements for the safety EGR and the leancombustion, it is known that it's preferable to increase the burningvelocity.

In order to raise this burning velocity, there have been recentlyproposed several suction systems, in which a sub-suction path providedseparately from a main suction path is designed to inject a gas into acombustion chamber, thereby generating a swirl of the suction gas in thecombustion chamber.

However, the suction system provided with such a sub-suction path is ina transient range to the practical use and has much to depend upon thefuture investigation. In the conventional suction system, indeed, sincethe intensity of the swirl generated is not sufficient, there arises alimit to the lean combustion and considerable improvement in the rate offuel consumption cannot be expected, if the heavy EGR is performed whiletaking preference of measures for the exhaust emission control,especially, the reduction in the NO_(X) emission.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide aninternal combustion engine which can enable a heavy EGR and leancombustion for the purposes of improvement in rate of fuel consumptionand reduction in the noxious gas emission by the strong swirl generationthrough a sub-suction path provided separately from a main suction path.

Specifically, it is an object of the present invention to provide aninternal combustion engine, in which the opened direction of the outletend of a sub-suction path is set within such a range that, in a planenormal to the axis of the cylindrer, the line extending in an openeddirection of a sub-suction path is at an angle of ±20 to 110 degreeswith respect to the line joining the center of a suction port and theaxis of an engine cylinder, whereby a more intense swirl in the suctiongas can be generated to enhance the limit of the lean combustion.

Another object of the present invention is to provide an internalcombustion engine, in which the distance between the outlet end of asub-suction path and the face of an suction valve at its closed position(a valve facing circle of a valve seat of the suction valve) is made notmore than the internal diameter of a main suction path, whereby a moreintense swirl in the suction gas can be generated to raise the limit ofthe lean combustion.

Still another object of the present invention is to provide an internalcombustion engine, in which the outlet end of a sub-suction path ispositioned within a sphere with its center being the spark point of anignition plug and with the same diameter as the internal diameter of thecylinder and within a range of ±1 mm from a plane which contains boththe center line of a stem of a suction valve and such one of thecontacts of tangency between a valve facing circle of a valve seat of asuction valve and a lines drawn from the spark point of the ignitionplug as is nearer to the wall of the cylinder, whereby a more intenseswirl of the suction gas can be generated to enhance the limit of thelean combustion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing one embodiment of the presentinvention;

FIG. 2 is an enlarged sectional view showing an essential portion ofFIG. 1;

FIGS. 3 to 5 and FIG. 8 are schematic views showing the opened directionof the outlet end of a sub-suction path, as viewed from the inside of acylinder head;

FIGS. 6, 7 and 9 are graphs illustrating the effects of the presentinvention;

FIGS. 10 to 12 show another embodiment constructing the outlet endportion of a sub-suction path, FIG. 10 being a view showing the cylinderhead, as viewed from the inside thereof, FIG. 11 being a viewcorresponding to FIG. 2, and FIG. 12 being a front elevation showing apipe member;

FIG. 13 is an enlarged sectional view showing an essential portion ofstill another embodiment of the present invention;

FIGS. 14 and 15 are graphs illustrating the effects of the internalcombustion engine shown in FIG. 13;

FIG. 16 is a schematic view showing an internal combustion engineaccording to still another embodiment of the present invention;

FIG. 17 is longitudinal section showing an essential portion of theinternal combustion engine in FIG. 16.

FIG. 18 is an enlarged longitudinal section showing the positionalrelationship between a sub-suction path and a spark point of an ignitionplug shown in FIG. 17;

FIG. 19 is a top plan view showing the positional relationship betweenthe sub-suction path and an cylinder shown in FIG. 18;

FIG. 20 is a graph illustrating the relationship between an air-fuel(A/F) ratio within the stable combustion limit of the internalcombustion engine according to the present invention and a distance l,and

FIG. 21 is a graph illustrating the relationship between the air-fuel(A/F) ratio within the stable combustion limit of the internalcombustion engine according to the present invention and a distance n.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in connection with theembodiments thereof with reference to the accompanying drawings. In FIG.1, reference numerals 1 and 2 indicate a cylinder and a cylinder head,respectively. Numeral 3 indicates a piston which is fitted in thecylinder 1. Numeral 4 indicates a combustion chamber which is defined bythose engine components 1, 2 and 3 and into which a main suction path 5is opened. Thus main suction path 5 is constructed as a passage whichleads from an suction port 6 formed in the cylinder head 2 via a suctionmanifold 7 and a two-barrel carburetor 8 acting as a fuel supply deviceto an air cleaner 9.

The outlet end of the suction port 6, i.e., the open end opened into thecombustion chamber 4 is equipped with an suction valve 10, by which thesuction port 6 is opened or closed. On the other hand, an exhaust port11 formed in the cylinder head 2 is opened or closed by an exhaust valve12. Both the aforementioned two valves 10 and 12 are controlled by theaction of an opening control mechanism, which is constructed by returnsprings 13 and 14, cams 16 and 17 and rocker arms 18 and 19 which are tobe driven by a cam shaft 15 and so on so that they are seated upon theirrespective valve seats 20 and 21 when they are closed.

Reference numeral 22 indicates a sub-suction path which has a smallereffective opening area than that of the main suction path 5. Thesub-suction path 22 is constructed of: a pipe member 22A which ispress-fitted in the cylinder head 2 thereby to constitute the outlet endportion of the sub-suction path; a passage portion 22B which is formedin the suction manifold; a passage portion 22C which is formed in thebody 8a of the carburetor 8; and two inlet ends 22D and 22E which arebranched from the passage portion 22C and which are respectively openedinto the primary passage portion 8b of the carburetor 8. Both the twoinlet ends 22D and 22E are spaced in the flow direction of the passageportion 8b. Specifically, the upstream side inlet end 22D is openedbetween a primary venturi portion 8c and a primary throttle valve 8d ofthe carburetor 8 whereas a downstream side inlet end 22E is opened atsuch a position as is closed by the primary throttle valve 8d at itsclosed (i.e, idling) position.

On the other hand, as shown also in FIG. 2 the pipe member 22Aconstituting the outlet end portion (i.e., the end portion at the sideof the combustion chamber 4) of the sub-suction path 22 has an injectionnozzle portion 22a with a reduced diameter which is fitted in thecylinder head 1 such that it is opened to protrude into the suction port6 upstream of the suction valve 10. On the other hand, the remainingbase end portion of the pipe member 22A forms a bore portion 22b whichis press-fitted in a fitting hole 2a formed in the cylinder head 2. Thisfitting hole 2a has its on end opened into the suction port 6 and itsother end opened into the fitting side of the suction manifold 7. Thepipe member 22A may be forced into the fitting hole 2a from the suctionmanifold fitting side. Moreover, the injection nozzle portion 22a of thepipe member 22A thus constructed is designed to generate a swirl of thesuction gas on the axis of the cylinder 1 in the combustion chamber 4when a gas is injected from the nozzle. The oriented direction of theinjection nozzle portion 22a is so set as to generate an intense swirlof the suction gas, as will be described hereinafter.

Here, the oriented direction of the aforementioned injection nozzleportion 22a as a first embodiment i.e., the opened direction of theoutlet end of the sub-suction path 22 will be described in detail withreference to FIG. 3. Now, the axis of the cylinder 1 is denoted at 0,the center of the portion of the suction port 6, which is opened intothe combustion chamber 4, is denoted at I, and the line joining thosetwo centers if denoted as L. In a plane P (which should be referred toFIG. 2) normal to the axis 0 of the cylinder 1, the injection nozzleportion 22a is directed such that the projected line on this plane ofthe line extending through the aforementioned center I is at an angle of±20 to 110 degrees with respect to the joining line L. The directionrange thus defined is represented by a central angle θ and illustratedby a fretwork in FIG. 3. On the other hand, FIGS. 4 and 5 illustrate thearrangements which are slightly different in the positionalrelationships of the suction and exhaust ports 6 and 11 and an ignitionplug 23 from that of FIG. 3. Nevertheless, the oriented direction of theinjection nozzle portion 22a is similar to that shown in FIG. 3.

Incidentally, the exhaust gases is recirculated from the exhaust path 22via an EGR valve into either the main suction path 5 or the sub-suctionpath 22. Nevertheless, the constructions of the EGR path and the EGRvalve can be made same as or similar to those of the prior art, andtherefore, explanation thereof are omitted.

In the internal combustion engine having the construction thus fardescribed, during the suction stroke having the suction valve 10 opened,the combustion chamber 4 is supplied with an air-fuel mixture from themain suction path 5, whereas a gas (e.g., the air or its mixture) isinjected (or sucked) from the sub-suction path 22 into the combustionchamber 4 through the clearance between the suction valve 10 and thevalve seat 20. By the injection of the gas from that sub-suction path22, the mixture sucked into the combustion chamber 4 is supplied withswirl around the axis of the cylinder 1 so that the burning velocity maybe accelerated.

Since the oriented direction of the injection nozzle portion 22a is setin the aforementioned manner, (according to the present invention, theintensity of the swirl generated becomes so high that the engine can berun with a far larger A/F ratio than the prior art even in case the EGRis performed at the same rate. This effect of the present invention isillustrated in FIG. 6. From this Figure, it will be understood that thelean combustion limit can be more effectively raised if the swirlingdirection is made such that the swirl flows into the exhaust port afterit has swept the ignition plug 23.

Moreover, it is preferable that the direction of the injection nozzleportion 22a is set in the following manner. With reference to FIG. 8,specifically, in the plane P normal to the axis of the cylinder 1, thewall portion of the cylinder, which is the nearest to the ignition plug23, i.e., the point on the circle of the cylinder wall which is nearestto the ignition plug is denoted at X, and the line joining this nearestpoint and the injection end of the injection nozzle portion 22a isdenoted at L'. Then, it is preferable that the direction of theinjection nozzle portion 22a is set within a range of ±30 degrees withrespect to the aforementioned joining line L'. This direction range isdefined by an angle θ' and illustrated by a fretwork in FIG. 8. Theresultant effect is illustrated in FIG. 9, from which it is understoodthat the oriented direction as shown in FIG. 8 is perferred forenhancement of the lean combustion limit.

Moreover, the oriented direction of the injection nozzle portion 22a isalso preferred to be set within a predetermined angular range withrespect to the plane P normal to the axis of the cylinder 1. Revertingto FIG. 2, the oriented direction of the injection nozzle portion 22a isset within a range of an angle of 15 to 30 degrees toward the piston 3with respect to the aforementioned plane P. Incidentally, this directionrange is defined by an angle α in FIG. 2. The resultant effect isillustrated in FIG. 7.

Now, the concrete constructions for directing the injection nozzleportion 22a in the aforementioned manners will be described in detail inthe following. According to one example, the pipe member 22A isconstructed such that the injection nozzle portion 22a of the pipemember 22A is formed into a bent shape with respect to a bore portion22b, as shown in FIG. 2. In this case, the bore portion 22b of the pipemember 22A can be extended in parallel with the plane P normal to theaxis of the cylinder and at a right angle with respect to a crank-shaft(not shown) which extends at a right angle to the sheet drawing FIG. 2with the advantageous result that the operation of boring the fittinghole 2a in the cylinder head 2 can be facilitated.

Still another example of the concrete constructions is shown in FIGS. 10to 12. According to this example, the pipe member 22A is formed into astraight shape as a whole, i.e., formed such that the two portions 22aand 22b are made coaxial. In this case, the fitting hole 2a is bored inalignment with the oriented direction of the injection nozzle portion22a. According to this example, the injection nozzle portion 22a can beoriented in any desired direction merely by forcing the pipe member 22Ainto the fitting hole 2a without considering the deviation in acircumferential direction of the pipe member 22A on the axis thereof.

As is now apparent from the description thus far made, according to thepresent invention, the lean combustion limit can be enhanced to highlycontribute to the improvement in the rate of fuel consumption as well asthe exhaust gas purification.

Next, another embodiment which has been made as a result of variousinvestigations of the relationship between the position of the outletend of the sub-suction path and the swirl of the suction gas generated,in which the outlet end of the sub-suction path is opened immediatelyupstream of the suction valve for opening or closing the main suctionpath and in which the distance between said outlet end and the face ofthe intake valve at its closed position is made not more than theinternal diameter of the main suction path, will be described withreference to FIGS. 13 to 15.

In the present embodiment, the injection nozzle portion 22a constitutingthe outlet end portion of the sub-suction path 22 has a nozzle portionat an end thereof with a reduced diameter which is opened immediatelyupstream of the aforementioned suction valve 10. Moreover, the distanceS (see FIG. 13) between the leading end of that injection nozzle portion22a and the chamber side bottom face 20a of the suction valve seat 20 ismade smaller than the internal diameter D of the suction port 6,preferably, 10 mm or less. Needless to say, the injection nozzle portion22a is directed generally in the tangential direction of said cylinder 1so as to generate the swirl of the suction gas on the axis of thecylinder 1 within the combustion chamber 4, and the swirling directionis set such that the suction gas flows into the exhaust port 11 after ithas swept the ignition plug (not shown).

In the internal combustion engine having the construction thus fardescribed, during the suction stroke with the suction valve 10 opened,the mixed gas is supplied to the combustion chamber 4 from the mainsuction path 5, whereas a gas is sucked into and injected from thesub-suction path 22. By the injection of the gas from the sub-suctionpath 22, the air-fuel mixture sucked into the combustion chamber 4 isswirled around the axis of the cylinder 1 so that the burning velocityis accelerated.

Here, in the present invention, since the aforementioned distance S isset at the aforementioned value, the generated swirl of the suction gasis intensified so that the lean combustion limit is enhanced, i.e., sothat a stable combustion can be ensured at a higher air-fuel ratio thanthe prior art. These effects of the present invention are illustrated inFIGS. 14 and 15. FIGS. 14 and 15 are prepared at such an ignition timingas can generate the highest output power.

As is now apparent from the description thus far described, according tothe present invention, the lean combustion limit can be enhanced tohighly contribute to the improvement in the rate of fuel combustion aswell as exhaust gas purification.

FIGS. 16 to 21 show still another embodiment of the present invention.This embodiment is characterized in that the outlet end of theaforementioned sub-suction path is positioned within a sphere with itscenter being the spark point the ignition plug and with the samediameter as the internal diameter of the cylinder, and within a range of±1 mm from the plane which contains both the center line of the stem ofthe suction valve and such one of the contacts of tangency between thevalve facing circle of the valve seat of the suction valve and the linesdrawn from the spark point of the aforementioned ignition plug as isnearer to the wall of the cylinder.

Now, referring to FIG. 16, reference numeral 101 indicates a four-cycleengine. Numeral 102 indicates a main conduit acting as the suction path.Numerals 103 and 104 indicate a carburetor and an exhaust path. Numeral105 indicates a cylinder, into which the leading ends of the mainsuction path 102 and the exhaust path 104 are opened. Numeral 106indicates an ignition plug. Into the suction port of the cylinder 105,there is opened an sub-suction path 107 which is provided separately ofthe main suction path 102.

That sub-suction path 107 has its opened end 107 a positioned justupstream of a valve 108, as shown in FIG. 17, and oriented in thetangential direction of the wall of the cylinder 105, as shown in FIG.19. The positioning of the opened end 107a of the sub-suction path 107will be detailed by way of example with reference to FIGS. 18 and 19.The opened end 107a is positioned within a sphere 0₁ with its centerbeing the spark point P (which is indicated by a small circle in FIGS.18 and 19) of the ignition plug 106 and with the same diameter as theinternal diameter D of the cylinder, and in a space within a range of ±1mm from the plane S which contains both the center line of a valve stem108a and such one of the contacts of tangency, a, between the valvefacing circle 0₂ of a valve seat 109 and the lines, m, drawn from thespark point P of the ignition plug 106 as is nearer to the cylinderwall.

In fact, the sub-suction path 107 are provided commonly for the fourcylinders 105 and are connected with an air cleaner 111 via a confluentpipe 107b and an air flow control device 110. With the main suction path102, on the other hand, there is connected the base end of an exhaustgas recirculation path 113 which in turn is connected at its leading endwith the exhaust pipe 104 and at its midway with a controller 112 forcontrolling the exhaust gas recirculation rate. Numerals 114 and 115indicate a silencer and a tail pipe, respectively.

A conduit 116 is connected with the exhaust pipe 104 so that a secondaryair is supplied therethrough to the exhaust system. That conduit 116 isequipped at its midway with a reed valve 117, which is opened or closedby the use of the pulsations in the exhaust pressure so that thesecondary air may be efficiently introduced into the exhaust pipe 104.The supply of the secondary air may be alternatively introduced by anair pump in place of the read valve.

The internal combustion engine thus constructed according to the presentinvention operates in the following manners. Specifically, since thesub-suction paths 107 are connected with the air cleaner 111 through theconfluent path and the air flow control device 110 to be opened into theatomosphere, a high pressure difference is established during thesuction stroke. As a result, under a light load conditions in which theproperties of the air-fuel mixture are expecially deteriorated todegrade the combustion, the air is injected at a high speed from thesub-suction path 107 with a similar effect to that which could beobtained if the confluent path 107b were connected with a high pressuresource.

During an ordinal running operation, the flow rate of the mixturerequired to be supplied from the carburetor 103 via the main suctionpath to the cylinder 105 is one third of that during the full output atthe most. Thus, the opening of the throttle valve of the carburetor 103is considerably small. As a result, the pressure prevailing in the mainsuction path 102 is remarkably lowered to about one half of theatmosphere pressure. Consequently, the flow speed of the air injectedfrom the corresponding sub-suction path 107 is as high as a sonic level.The jet thus injected at that high speed generates an intense swirl inthat cylinder 105.

During the idling operation of the engine 101, to the contrary, sincethe engine 101 performs no work to the outside, the flow rate of themixture becomes so low that the pressure in the main suction path 102becomes far lower than the atmospheric pressure. Therefore, unless theair flow rate is adjusted to the optimum level by means of the air flowcontrol device 110, the proper mixture cannot be supplied so that thefuel consumption rate is augmented. This fuel consumption rate isdecreased by properly adjusting the air-fuel ratio to the theoreticalA/F ratio.

The exhaust gas is partially recirculated to the main suction path 102in accordance with the control of the controller 112 which is disposedin the EGR path 113. The combustion gas containing hydrocarbons HC andcarbon monoxide CO is exhausted from the exhaust path 104 to the outsideafter it has cleared of the HC and CO by the action of an oxidizingcatalyst which is mounted in the silencer 114. The air which may becomemore or less short for the oxidization of the exhaust gas is suppliedfrom the conduit 116.

Since, in the present invention, the suction gas flow is charged intothe tangential flow of the cylinder 105 by the action of the sub-suctionpath 107 and since the opened end 107d of the sub-suction path 107 is sopositioned that the tangential flow may give the largest effect, anintense swirl is generated in the cylinder 105 during the suction strokeof the engine 101 thereby to establish a vortex state. Although thatswirl is weakened during the compression stroke, such extremely fineturbulences as ensure the combustion can be maintained until theignition. Thanks to these turbulences, the burning velocity of themixture is accelerated to remarkably shorten the combustion time so thatthe stable combustion can be retained even under the much exhaust gasrecirculation. Moreover, the engine can be run even in the lean range ofthe mixture.

The influences of the turbulences upon the combustion play a remarkablyimportant role. In the existing engine, more specifically, the exhaustgas recirculation ratio allowed is about 10% at most, and the misfiretakes place, if the EGR ratio exceeds 10%, so that the stable combustioncannot be sustained any more. In other words, if the exhaust gasrecirculation ratio is excessively enlarged, the burning velocity isdecelerated so that an mis-firing is invited or so that the stablecombustion cannot be maintained.

To the contrary, if the swirl is so intensified as to augment theturbulences, a stable combustion can be maintained even for the muchexhaust gas recirculation. Thus, since the emission of the NO_(X) can benotably reduced, as compared with the prior art, the engine can be runat such an air-fuel ratio as to invite the most NO_(X) emission and atthe most proper burning timing (MBT). As a result, the fuel consumptionrate of the engine can be remarkably improved, as compared with thecombustion system according to the prior art.

This result is graphically illustrated in FIGS. 20 and 21 on theconditions that the r.p.m. of the engine is within most of the range forthe street running operation, the ignition timing is the highest outputpower producing timing, and the load is within the range for the streetrunning operation.

FIG. 20 illustrates the relationship in the stable combustion limitbetween the distance l (the ordinate) from the spark point P of theignition plug to the opened end 107a of the sub-suction path 107 and theair-fuel (A/F) ratio (the abscissa). According to FIG. 20, the air-fuel(A/F) ratio is shifted to the leaner side as the distance l approaches1/2 D from D, and the air-fuel (A/F) ratio is held almost constant from1/2 D to a distance l_(s), which is measured to the plane S containingthe center line of the valve stem 108a as shown in FIG. 18. According tothe present invention in which the opened end 107a is set at theaforementioned position, therefore, the engine can be run at a learnerside of the air-fuel ratio so that the fuel consumption rate can beimproved to a high level.

If the distance l becomes longer than 1/2 D, to the contrary, thesweeping action of the ignition plug is so deteriorated that theignition delay is augmented to elongate the burning time thereby todeteriorate the lean combustion limit. This is caused by the diffusionof the jet.

FIG. 21 illustrates the relationship in the stable combustion limitbetween the distance n (in ordinance) measured from the plane Scontaining the center line of the valve stem 108a in FIG. 18 to theopened end 107a of the sub-suction path 107 wherein the plane S is takenas "0", the side on which the ignition plug 106 is located is taken as"plus" and the side on which the ignition plug is not located is takenas "minus", and the air-fuel (A/F) ratio (in the abscissa).

It is judged that the nearer the position of the opened end 107a of thesub-suction path 107 is the inside of the combustion chamber, the moreeffective is the sub-suction path for producing the swirl. However, atthe plus side where that opened end is near the combustion chamber andit is apart more than 1 mm from the reference plane S ("0"), the jetwill impinge upon the valve seat 109 so that it diffuses. To thecontrary, at the minus side where that opened end is apart more than 1mm from the reference plane S, the jet will diffuse, before the jetpasses through the clearance between the valve and the valve seat 109,so that the swirl is weakened. As a result, the stable combustion limitcannot be attained at the air-fuel (A/F) ratio of a lean side. To thecontrary, since the swirl to be generated by the jet is intense with theposition of the opened end 107a of the sub-suction being locatedaccording to the present invention, the burning velocity is soaccelerated that the engine can be run at the air-fuel (A/F) ratio of alean side.

Here, it has been experimentally confirmed that the swirl in thecylinder 105 is intensified as the flow rate of the fluid to be suppliedfrom the sub-suction path 107 is increased. Nevertheless, since the flowrate of the mixed gas is low under the idling condition of the engine101 where the suction pressure is low, the air flow rate is suppressedto a relatively low level under the idling operation by means of the airflow control device 110 so that a misfiring can be avoided.

Since the present embodiment is constructed in the aforementionedmanners, the burning velocity of the mixed gas can be accelerated toshorten the burning time so that the lean combustion limit can beimproved to perform the exhaust gas recirculation at a high rate,whereby it is possible to reduce the noxious content of the NO_(X) andto improve the fuel consumption rate.

What is claimed is:
 1. In an internal combustion engine:a combustionchamber defined by a cylinder, a cylinder head and a piston fitting insaid cylinder; a main suction path having a suction port formed in saidcylinder head and adapted to be opened and closed by a suction valve atthe open end portion of said suction port which is opened into saidcombustion chamber; a sub-suction path, at least partially formed by astraight bore through the cylinder head, provided separately of saidmain suction path and having its outlet end opened immediately upstreamof said suction path; an exhaust port disposed opposite the suctionport, and an ignition plug disposed between the suction and exhaustports, wherein a swirling direction of gas injection from saidsub-suction path into said combustion chamber is directed such that aflow is toward the exhaust port after it has swept past the ignitionplug; wherein the improvement resides in that a direction in which theoutlet end of said sub-suction path opens is within a range of about 30degrees with respect to a plane extending normal to the axis of thecylinder, the plane including a line joining a point nearest on the wallof said cylinder from the ignition plug and the center of saidsub-suction port; wherein the direction is also at angle of 15 to 30degrees from a plane normal to the axis of the cylinder; and wherein anoutlet end portion is a pipe, press-fitted into the bore in the cylinderhead and having its leading end protruding into the suction port, theleading end being bent with respect to the bore in the cylinder head andthe internal diameter of the leading end portion being of a reduceddiameter with respect to the remainder of the pipe wherein the outletend portion is slightly laterally bent.